(1) Field of the Invention
The present invention relates to testing of sonar systems and more particularly, to a system and method for controlled simulation of a target underwater to test and evaluate a sonar system.
(2) Description of the Prior Art
Sonar systems transmit and receive underwater acoustic signals to locate targets such as underwater mines. A typical sonar system 10, FIG. 1, detects and locates a target 12 by transmitting an acoustic signal or ping 14. This acoustic signal 14 generated by the sonar system 10 is received by the target 12 and reflects back to the sonar system 10 as a reflected acoustic signal 16. In the reflected acoustic signal 16, the signal strength and wave structure is altered by the material characteristics of the target 12, i.e., the target vibrates and alters the shape of the reflected acoustic signal 16. The reflected acoustic signal 16 is received by the sonar system 10, and the sonar system 10 is able to determine distance information based upon the reflected acoustic signal 16.
One application of a sonar system is to locate and map mines underwater. Mine hunting systems and other underwater communications systems that transmit and receive underwater acoustic signals must be tested to measure the performance of these systems. One technique for testing these systems involves simulating an underwater target and determining whether or not the system can detect and locate the simulated target. Since there is little known about the acoustic properties of the target being detected, a sonar system is typically declared a success as long as it gets a reasonable response. If an underwater target cannot be detected, however, the evaluator may not know whether or not the failure lies with the test target or with the system being tested. For developers of sonar systems, a controlled test target is important to know if the system functions properly. Existing test systems acoustically reply back when interrogated by a sonar ping, but the reply has no characteristic of the original sonar signal nor is the reply a characteristic acoustic signature of a given underwater body. Underwater evaluation systems must provide a method of scoring and constructive feedback to the systems that are being tested.
Accordingly, one object of the present invention is to provide sonar systems with the capability of receiving a controlled response from an underwater target in order to gauge performance of the system.
Another object of the present invention is to provide a simulation system that can also act as a scoring system to maintain a record of hits and allow further systems evaluation.
The present invention features a target simulation system comprising a hydrophone for receiving an original acoustic test signal and converting the acoustic test signal to an analog electrical test signal. The signal processing system receives the analog electrical test signal, converts the analog electrical test signal to a digital test signal, modifies the digital test signal to form a simulated reflected signal emulating the original acoustic test signal reflecting from a target having a known target strength, and converts the simulated reflected signal to analog format. The projector receives the simulated reflected signal in analog format and converts the simulated reflected signal to a simulated reflected acoustic signal.
According to one preferred embodiment, the signal processing system includes an A/D converter for converting the analog electrical test signal to the digital test signal. A computer system is coupled to the A/D converter for modifying the digital test signal to form the simulated reflected signal emulating the original acoustic test signal reflecting from the target having a known target strength. A D/A converter is coupled to the computer system for converting the simulated reflected signal to analog format. The computer system can include a computer program for adding a target strength value to values of the digital test signal to form the simulated reflected signal. The computer system can also include a digital buffer for buffering the simulated reflected signal.
In one embodiment, the signal processing system further includes a signal detector coupled between the hydrophone and the A/D converter for detecting the analog electrical test signal and excluding other signals from detection. In one embodiment, the signal processing system can also include a power amplifier coupled between the projector and the D/A converter for amplifying the simulated reflected signal in analog format.
The present invention also features a method of generating a target simulation signal. The method comprises transmitting an acoustic test signal underwater. The acoustic test signal is received and converted to an analog electrical test signal. The analog electrical test signal is digitized to produce a digital test signal. The digital test signal is then modified to form a simulated reflected signal emulating the acoustic test signal reflected from a target having a known target strength. The simulated reflected signal is converted to analog format, is transmitted underwater, and is received underwater.
According to one method, the step of modifying the digital test signal includes converting the digital test signal into a series of ASCII numbers; receiving a target strength value; adding the target strength value to each of the ASCII numbers representing the digital test signal to produce an ASCII representation of the simulated reflected signal; and converting the ASCII representation of the simulated reflected signal.